Prompt gamma-ray
activation analysis (PGAA) provides a non-destructive means of simultaneously
determining the presence and amount of various elements in a sample. The
technique is relatively insensitive to the physical form of the sample, and no
special preparation, e.g. dissolving, atomization, etc., is
required. PGAA involves irradiating a sample with a collimated beam of
neutrons while concurrently observing production of gamma rays, which, in turn,
have energies characteristic of the elements from which they originated.

At the NCNR,
collimated neutron beams may be restricted in diameter by means of circular
apertures, and this in turn restricts the volume that is probed in a PGAA
measurement. However, reducing the size of the impinging neutron beam results
in a reduced production of gamma rays and subsequently longer acquisition
times. Therefore, a spatially resolved measurement using a very thin beam of
neutrons is impractical. However, it has been previously demonstrated that,
rather than restricting a beam using apertures, a neutron lens can be used to focus
a broad-diameter beam of cold neutrons onto a small spot. In this case, the
measurement can be restricted to a small volume without such a great loss in
count rate. The continuation of an earlier project using a neutron lens to
provide mm3-spatial resolution technique will be described.